The present invention relates to a method and apparatus of continuously measuring the concentration of at least one component in a gas sample. More particularly, the present invention relates to such a method and apparatus which employs a laser for charging the gas sample with radiation at a frequency in the range of an absorption line of the component, a detector device for receiving a measurement signal corresponding to the intensity of the transmitted radiation, as well as an evaluation circuit and devices for performing the measurements.
A method of the above type is disclosed in Federal Republic of Germany DE-OS No. 3,510,052. However, in the described process the absorption line must be tuned by way of a variation in temperature, and the absorption must be measured at a harmonic of the activated molecule.
The problem of continuously and selectively measuring specific trace gas concentrations, particularly of HF, exists particularly in industry. Solutions have been attempted wich provide for the use of wet chemical analysis methods. While such methods do provide accurate analysis values, they do not permit real time detection and control. Physical processes employing spectrally broadbanded light sources have also been employed which, however, do not permit selective measurements due to transverse sensitivity to water lines. Or, ultimately, laser spectroscopy has been utilized which operates with lead salt diode lasers. The latter, due to the necessity of low operating temperatures (15.degree.-150.degree. K.), require expensive helium cooling elements.
The last mentioned lead salt diode laser spectrometers are expensive since they require expensive He cooling elements. Moreover, the lead salt diode laser is a multimode laser, and thus involves additional expenditures (monochromator) to provide for wavelength selection in the beam path. The same applies for devices with In, Ga, or As/GaAs operating in the room temperature range. They also require a monochromator for wavelength selection, are all equipped with exclusively prismatic beam dividers to split the beam into a reference beam and a measuring beam, and use a multichannel boxcar integrator system for signal processing.